Coated smokeless powder



Unite to i1 tent .fific Patented Dec. 23, 195

COATED SMOKELESS POWDER Jack J. Foster, Alton, and Joseph M. Allovio, Wood River, 1., assignors to Olin Mathieson Chemical Corporation, East Alton, 111., a corporation of Virginia N Drawing. Application April 12, 1955 Serial No. 500,992

2 Claims. (Cl. 52-7) This invention relates generally to explosives and more particularly to smokeless powder grains having improved ballistic characteristics.

A method for making substantially spherical smokeless powder grains is disclosed in Olsen et al. patent, U. S. 2,027,114, and a method for making dense powder grains of this general type is disclosed by Schaefer in U. S. Patent 2,160,626. The powder grains made in accordance with these processes have been widely adopted for use in both military and commercial cartridges. Cartridges having powder charges composed of such powder grains have many advantages but in many instances it has been necessary to roll the grains in order to obtain the required ballistic characteristics in certain cartridges. Furthermore, in some cartridges, particularly those made for use in match competition where uniform accuracy, velocity, pressure and other ballistic characteristics are a requisite, it I has been found that cartridges containing such powder charges are frequently unsuitable. This disadvantageous property is most apparent when cartridges are fired in a gun pointed downwardly and the powder is positioned near the bullet and away from the primer. Often be- 1 cause of these disadvantages, it has been impossible to 1 use the same propellant in cartridges of different calibers and in some instances, it has been impossible to use powder from the same lot in cartridges of the same caliber but having different types of projectiles. It is therefore an object of this invention to provide a 1 novel smokeless powder grain having improved ballistic characteristics. Another object of this invention is to provide smokeless powder grains particularly well suited for cartridges used in match competition and other cartridges where uniform ballistic properties are requisite. Still another object is to provide substantially spherical smokeless powder grains having such ballistic properties that cartridges of various calibers can be charged therewith and uniformity in ballistic properties will be attained.

The foregoing objects as Well as others which will become apparent from the following description are achieved in accordance with this invention, generally speaking, by providing smokeless powder grains having a surface coat- .ing of a finely divided metallic oxide. Tin dioxide has been found particularly well suited for this purpose. The :surface coating must be substantially uniformly distributed over the surfaces of the grains. The particles of tin :dioxide are only partially embedded in the grains so that the greater portion of their surface is uncoated and protrudes from the grain. There is no material advantage in including any metallic oxide in the internal portion of the grain, insofar as this invention is concerned. It is preferred to include a potassium salt in the coating as a flash inhibitor because the mixture of the potassium salt with the tin dioxide results in the best ballistic performance but in some powders the potassium salt can be incorporated uniformly throughout the grain. Any potassium salt of the proper granulation which will improve the ignition properties of the powder grains such as potassium nitrate and potassium sulfate or mixtures thereof can be utilized. From about 0.3 to about 1.5 parts by weight of tin dioxide should be used and in those powders containing a potassium salt from 0.3 to about 1.5 parts thereof should also be used. The granulation of the potas- 5 sium salt and the tin dioxide must be less than about 325 mesh, U. S. Tyler screen, or in other words less than about 44 microns. The coating is advantageous on any smoke less powder grains including grains formed from nitrocellulose base and double base smokeless powder grains formed from nitrocellulose and nitroglycerin or other liquid explosive nitric ester.

In a specific example of this invention, about 100 parts 'by weight substantially spherical nitrocellulose base powder grains formed in accordance with the process disclosed in U. S. 2,160,626 are impregnated with nitroglycerin and coated with a deterrent, dibutylphthalate. The composition of the grains is about 83 percent nitrocellulose, percent nitroglycerin, 6 percent dibutylphthalate and one percent diphenylamine. These grains are placed in a sweetie barrel and a solution of about one part potassium nitrate and 1% parts tin dioxide suspended in about parts isopropyl alcohol is poured over the grains and the mixture is tumbled until a substantially uniform coating has been applied to the surface of each grain. Ordinarily, a uniform coating is obtained by heating the contents of the barrel to about 50 C. and tumbling them for about one hour. Tumbling is continued at this temperature another 45 minutes to remove the isopropyl alcohol. The granulation of the potassium nitrate and of the tin dioxide in this embodiment is:

Percent By Weight Below Size Shown Stokes Diameter Microns The granulation of the potassium salt and tin dioxide recorded above was determined by sedimentation analysis.

Powder grains having a diameter of between 0.16" and 0.025" made in accordance with the foregoing process were charged in caliber .30 cartridges and fired in comparison with substantially identical cartridges except that the powder charge in the latter cartridges did not have a coating of the potassium nitrate and tin dioxide. Otherwise the composition of the smokeless powder grains in the two groups of cartridges was substantially the same. The following results were obtained when the cartridges were fired in a gun in a substantially horizontal position and the velocity of the projectile was measured in feet per second: Table I Ball Cartridges Armor Piercing Cartridges Sam 1e Sample Sample Sample No. 1 No.2 No.3 No.4

Grains Grains Grains Grains Charge Weight 51. 53. 3 53 54. Mean Velocity 2720 2725 2708 2721 Maximum Velocit 2754 2750 2735 2733 Minimum Velocit 2668 2698 2685 2707 Extreme Variation 86 52 50 26 Std. Deviation 22. 9 15. 6 16. 4 8. s

to provide a mean velocity within the range required by standard specifications for that cartridge. By comparing samples 1 and 2 it is found that the extreme variation in velocity from one cartridge to another in the series fired was 86 feet per second when powder not having the coating provided by this invention was used. The extreme variation was only 52 feet per second'in -the ball'cartridges when powder of this invention wasused. Variation in velocity in the armor piercing cartridges making up sample No. 3 and having heretofore conventional powder was 50 feet per second whereas the variation in sample No. 4 having the powder of this'invention was only 26 feet per second. Possibly of more significance tothe ballistician is the difference between the standard deviation of the samples. These results show conclusively that the powders of this invention give more uniform velocity results than the conventional powders. The standard deviation is a calculated value customarily used by those skilled in the art as a criterion of ballistic uniformity. This value is obtained by taking the square root of the sum of the squares of the differences between the individual values in a series and the average of values in the series.

In some rifle cartridges the case volume is greater than is required for the powder charge so that the powder charge does not completely fill the available space. As a result, when the gun has its muzzle pointed downwardly there is a tendency for the powder to accumulate at the base of the projectile in the cartridge. Conversely, if the gun is pointed upwardly the powder accumulates at the primer. When the heretofore available powders have been used, the velocity variation between cartridges fired with the powder charge located adjacent to the base of the projectile and at the primer or with the gun in a horizontal position has been appreciable and objectionable. This difference in velocity is less with the powder of this invention as is shown in the following table:

The cartridges of sample #1 contained conventional powder and sample #2 was composed of cartridges containing powder of the same composition except that the grains were surface coated in accordance with this invention. The velocity obtained when cartridges of sample #1 were fired with the powder adjacent to the bullet was 105 feet per second lower than the velocity of cartridges fired with the powder adjacent to the primer'whereas only 43 feet per second difference was found with the cartridges of sample #2. Such results show that orientation of the powder in the cartridge is less effective on the velocity of the cartridge when the powder of this invention is used in preference to the heretofore'conventional powders.

It is also to be noted that the performance of cartridges having the powder charge provided by this invention is superior to similar cartridges having uncoated powder grains in the standard hangfire test. This test involves measuringthe period of time which elapses between initiation of the primer and ignition of the powder and it has been found that in cartridges which have been cooled to -34 F. an average time of 0.5 millisecondelapses' between the initiation of the primer and ignition of the powder in the cartridges not having the coating provided by this invention whereas only 0.38 millisecond elapses with the cartridges having the powder charge of this invention. This characteristic is a very important one and the results of this test indicate that a significant improvement is obtained by coating the grainsin accordancefwith this invention. Comparison of the results shown in Table III below illustrate that the powder having the coating provided by this invention is less effected by orientation within the cartridge than powders in which the tin dioxide has been incorporated throughout the grains structure. The velocities are reported in feet per second. Sample No. 1 was made up of cartridges loaded with powder grains having 1.25 percent tin dioxide incorporated therein whereas sample No. 2 was composed of cartridges loaded with powder coated with 1.25 percent tin dioxide as provided by this invention. The powders used in the samples were otherwise of the same composition containing about 83 percent nitrocellulose, 10 percent nitroglycerin, 6 percent dibutylphthalate and 1 percent diphenylamine before treating with tin dioxide. A difference of only 49 feet per second was obtained between cartridges having the powder -adjacent the primer and cartridges having the powder adjacent the bullet when the powder was of the type provided by this invention whereas a difference of feet per second was obtained under similar conditions with a powder in which the tin was incorporated substantially uniformly throughout the grain. These results show that the powder having the tin dioxide incorporated therein was no better than the conventional powder not containing tin dioxide reported in Table II as sample No. 1.

The results shown in Table-1V below illustrate that powders having tin dioxide incorporated therein do not give results comparable to those results obtained with powders having a coating of tin dioxide. The two samples here were from the same lot as samples No. 1 and No. 2 in Table III with sample No. 1 having 1.25 percent tin dioxide dispersed uniformly in the grain and sample No. 2 having a coating of 1.25 percent tin dioxide. Comparison of the extreme variation and the standard deviation results of these two samples clearly illustrates that a much more uniform velocity was obtained with powders of this invention than with powders containing the tin dioxide within the grain.

The powder grains provided by this invention and one method for making them have been described in considerable detail in the foregoing for the purposes of illustration. It is, of course, to be understood that any suitable process for coating the grains can be utilized and that various liquid carriers can be substituted for the isopropyl'alcohol. For example ethyl alcohol, methyl alcohol, benzoyl, toluene, gasoline or any other non-solvent for the smokeless powder grains and for the particles of the potassium salt and the tin dioxide which can be removed from the grains can be utilized. Although the detail description was made" with respect to substantially spherical powder grains formed by the process disclosed in U. S. Patent 2,160,626, the coating is advantageous on powder grains made by other processes such as extrusion processes and on grains'bf any suitable shape;

Many other variations in the invention will occur to those skilled in the art and can be used without departing from the scope of this invention except as it is limited by the appended claims.

We claim:

1. A substantially spherical smokeless powder grain consisting of a nitrocellulose propellent core with a coating of tin dioxide on the surface thereof, said tin dioxide being present in the amount of from about 0.3 to about 1.5 parts by weight per each 100 parts by weight of said 10 2,038,700

grain.

References Cited in the file of this patent UNITED STATES PATENTS Woodbridge Apr. 28, 1936 2,304,037 Kilmarnock et a1 Dec. 1, 1942 

1. A SUBSTANTIALLY SPHERICAL SMOKELESS POWDER GRAIN CONSISTING OF A NITROCELLULOSE PROPELLENT CORE WITH A COATING OF TIN DIOXIDE ON THE SURFACE THEREOF, SAID TIN DIOXIDE BEING PRESENT IN THE AMOUNT OF FROM ABOUT 0.3 TO ABOUT 1.5 PARTS BY WEIGHTY PER EACH 100 PARTS BY WEIGHT OF SAID GRAIN. 